The present invention relates to an underwater trenching system, and more particularly, to a trench making equipment that enlarges an underwater trench for burying a pipeline.
Many oil and gas production sites require installation of miles of pipelines for delivery of the produced material to a refinery or other destination. Often times, the pipelines are laid underwater, especially in shallow coastal waters. The pipes are usually buried at the bottom of a waterway, such as a river, marsh, or sea. In some locations, the pipes are simply laid along the bottom of a waterway and left exposed, to be buried by the action of the currents. In other uses, a trenching tool, such as a water jet, a cutter head, or a scoop, or clam shell digger digs a trench around the pipe, which then settles into the trench.
The bottom sediment eventually settles around the pipe although a large portion of it is carried to other areas of the waterway. The time when the sediment remain in suspension varies although it is known to have a potential for creating serious environmental damage to plants, animals, marine life, and the water. Over time, the sediment has a tendency to shift the pipeline, which causes it to rise from the bottom or from the trench. Current governmental regulations prohibit disturbing the waterway bottom for the second time, such that digging out the original trench for adjusting position of the pipeline is not a viable option. As a consequence, the only viable alternative is to excavate the side of the trench near the bottom and cause the pipeline to drop into the new indentation in the soil.
In short, all currently known equipment and methods for underwater trenching create large clouds of silt and debris that remain in suspension for a long time and seriously disrupt the ecology of the waterway. Reforming the trench by additional excavation of the bottom is not allowed.
There exists therefore a need for an underwater trenching system that avoids bottom trenching, while achieving the goal of lowering the pipeline into a trench without excavating the bottom of the trench.